mid-14c., from Late Latin mediatorem (nominative mediator) "one who mediates," agent noun from past participle stem of mediari "to intervene, mediate," also "to be or divide in the middle," from Latin medius "in the middle" (see medial (adj.)). Originally applied to Christ, who in Christian theology "mediates" between God and man. Meaning "one who intervenes between two disputing parties" is first attested late 14c. Feminine form mediatrix (originally of the Virgin Mary) from c.1400. Related: Mediatorial; mediatory.